Collapsible Dobsonian Mount

chrisyeo · Post by **chrisyeo** » Wed Nov 03, 2004 1:49 am

Hi,

I've been planning to get a carpenter to fabricate a collapsible dobsonian mount for my 6" F5. The design is copied from 1stbase telescopes:

I'd like to share the idea and ask for some comments: is it feasible, and how much would it cost?

[web]http://www.singastro.org/album_pic.php?pic_id=300[/web]

The base can be folded up in the following way:

[web]http://www.singastro.org/album_pic.php?pic_id=301[/web]
If it looks confusing, you can click here to see a sequence of photos.

The mount has two tricky parts. First is the edge that connects part B and C. For the hinge to work properly, the edges must be sawed off at a 45 degree angle.

Secondly, the knobs that secure the pieces together looks rather difficult to make. Instead, my idea is to drill a 1/4" hole at a 45 degree angle through the corners and use a 3" bolt to screw the corners together. A wingnut makes the bolt removable:

[web]http://www.singastro.org/album_pic.php?pic_id=302[/web]
A total of four of these need to be drilled.

Will it work? Can it be made?

If I use 1/4" plywood and the mount is approximately 1 foot by 1 foot by 2 feet high, how much do you think it will cost?

Thanks for your comments!

Chris

p/s. Apologies for the funny pictures. The [img] tag doesn't seem to work

MooEy · Post by **MooEy** » Sun Nov 07, 2004 5:27 pm

hmm..i just noticed the 45 degrees cut. since u said u are getting a carpenter to do it, y not just let him cut it at 45 degrees. think it shouldn't be too hard for someone with experience.

~MooEy~

Post by **weixing** » Sun Nov 07, 2004 7:32 pm

Hi,
Is part A a single piece?? If yes, then the height of part A is limited by the aperture of your scope.. right? Or it will not be able to fold down. This mean that you may have problem balancing your scope...Although can be solve by adding counter-weight at the primary mirror side of the scope, but will need to bring counter-weight.

First is the edge that connects part B and C. For the hinge to work properly, the edges must be sawed off at a 45 degree angle.

The carpenter should be able to do it for you.

Secondly, the knobs that secure the pieces together looks rather difficult to make. Instead, my idea is to drill a 1/4" hole at a 45 degree angle through the corners and use a 3" bolt to screw the corners together. A wingnut makes the bolt removable:

The plywood may break if you tighten the wingnut too much, because the bolt and nut is asserting force at an angle and the plywood is only 1/4" thick.

Overall, the design look quite weak. It may work if you use a thicker and stronger wood, but I think 1/4" plywood may not work.

Anyway, I suggest you may consider have something to secure part B and the base together, so that the whole base will be stronger.

Have a nice day.

chrisyeo · Post by **chrisyeo** » Mon Nov 08, 2004 1:32 am

Hi Weixing!

Is part A a single piece?? If yes, then the height of part A is limited by the aperture of your scope.. right? Or it will not be able to fold down. This mean that you may have problem balancing your scope...Although can be solve by adding counter-weight at the primary mirror side of the scope, but will need to bring counter-weight.

Yes, part A is a single piece, but I don't understand why it has anything to do with the aperture or the balance. If you look at these pictures maybe you'll get a better idea:
http://www.astronomy-mall.com/FirstBase/collapse1.html

The plywood may break if you tighten the wingnut too much, because the bolt and nut is asserting force at an angle and the plywood is only 1/4" thick.

The screws need not be tightened too much, they only need to hold the structure rigid so that the scope can sit stable on top. Also, the 6" scope I plan to put on top is quite light, so 1/4" should be able to hold it up. I think for larger scopes need to use 1/2" but that might increase its weight unnecessarily.

Maybe I should drill two more holes to secure part B and the base together. Thanks for the suggestion!

Chris

chrisyeo · Post by **chrisyeo** » Mon Nov 08, 2004 1:35 am

hmm..i just noticed the 45 degrees cut. since u said u are getting a carpenter to do it, y not just let him cut it at 45 degrees. think it shouldn't be too hard for someone with experience.

If the carpenter is able do it, I'll just ask them to cut and drill the parts for me. I can assemble the rest myself.

Does anyone have experience with a carpenter and knows how much it might cost? Kayheem?

Chris

Post by **weixing** » Mon Nov 08, 2004 7:56 am

Hi,
Opps :oops: I see wrongly (my eye got "stamp" ha ha ha)... It is folding to the side... I thought it is folding down.

Anyway, I would still suggest you use a solid wood instead of plywood... I really don't think plywood is suitable since the thickness is only 1/4".

By the way, I think there are a few type of plywood and you should use a more weather proof plywood which use a Water-resistant adhesives and can resist a certain amount of moisture.

Have a nice day.

dan · Post by **dan** » Mon Nov 08, 2004 4:05 pm

Hi Chris,

Try this wood supplier:
Willwin Tropical Produce Co
Blk1057 #01-85 Eunos Ave 3
Tel:67480446

They supply in whole plank (8'X4'). You have to prepare the diagram layout before they can quote you the price with cutting. You don’t need the whole piece, so the price will be much cheaper.

The joining part with bolt and wing-nuts would have gaps when tighten, why don’t use hinges to secure the A and D parts?

Dan

MCYM · Post by **MCYM** » Mon Nov 08, 2004 6:53 pm

Hi Chris

That is a commendable attempt to make a collapsible dob-base mount. Remember to show us the completed product.

Ask for marine grade ply if you have not begin to build one. These sheets have no void and gaps between the plys-end also
it will look nice cosmetically when finish.

IMHO you will have better results sticking to large thumbscrews as fastener. At least the manufacturer is using them with success.
Drop me a line if you are interested to take this route.

Cheers

Matthew

ariefm71 · Post by **ariefm71** » Tue Nov 09, 2004 12:02 am

If the carpenter is able do it, I'll just ask them to cut and drill the parts for me. I can assemble the rest myself.

Does anyone have experience with a carpenter and knows how much it might cost? Kayheem?

Chris

Machinist:
Ong Yeok Jin (he's one of the bosses)
PQS (company name)
3006 Ubi Rd 1 #04-354
Tel: 68424356

Woodwork:
Soo Tiong Beng (boss) Company name is boss' name.
18 Defu Lane 7
Tel: 62845882

Alternatively, you can look up both the usual yellow pages as well as in the Commerical & Industrial Guide under the heading "Woodworkers". Call them up and see if they do small jobs.

river · Post by **river** » Wed Jul 13, 2005 2:25 pm

Hi Chris,
It will be fun to make a base for dob. I like to make a few suggestion,

:: To hold the scope.
1) The carpenter should have the power saw that can cut semi circle at the top of part A and part C. (see the link you gave to weixing)
-- if you put a circle onto V cutting, you only have 2 point contact, semi circle that better fit your OTA provide better grip.
Why? the opening end might "drop down" once you let it go or when you add some extra parts on the secondary opening.

:: to joint part A and part C.
2) Another way is to replacing the part B with a few small metal rods that have screw thread at both ends. Drill hole at part A and part C, on the field, screw part A and part C to the rods.

Bosch have lots of fancy rod, screw etc. they have a warehouse at Jalan Pemimpin, near Bishan. They can cut, make screw thread for you.

Have fun